Listening to an Eluvium record is like staring at a river. It moves, but it doesn’t really go anywhere. While you stand still in front of it, waiting for something interesting to happen, you suddenly realize that your mind is flowing along with it. You watch your thoughts and feelings float by in the water, at enough of a distance that you can’t distinguish them well enough to call them by their names. Ambient music is suggestive, like poetry; it can sometimes trick writers into saying too much about what’s not really there instead of treating the music as what it is: a deliberate arrangement of sounds. Perhaps this confusion is the goal of figurative language; when a simile works well, it hides its own machinery. You hear “eyes like stars,” and you forget the word “like,” then you forget both the eyes and the stars; the objects blend together in your mind into something unique and impossible.

Matthew Cooper has challenged himself with this record, adding sung lyrics and percussion to music that has always been instrumental and beatless. For those who have followed his recording career for any length of time, this change might seem jarring, a small revolution, but when his hushed baritone arrives on the scene in the lead track “Leaves Eclipse the Light,” the development sounds completely natural. The voice enters from within the song, not from above or outside it. And the words aren’t moody or romantic, like the unwelcome veneer of the lite orchestral sounds on his 2007 album Copia; these lyrics are placid, vague, and reflective, sitting low in the mix like an anchor. Cooper has not abandoned his old aesthetic, which blends separate elements of sound together like the events in a dream, but ever since he stepped away from the deliberate and all-encompassing textural shadowiness of 2005’s Talk Amongst the Trees, the harmony has existed more in the careful balance within the arrangements than in an actual blurring of distinctions between sounds. And in spite of the “pop” structure of the vocal songs, the added shifts in dynamics, and the motion between different sections and melodies, these pieces still feel like rivers; they move, but without going anywhere.

From the layered and melody-rich vocal tracks to the humble, monochromatic instrumental interludes, Similes remains firmly rooted in Eluvium’s single-minded optimism. Even in tracks with titles like “Weird Creatures” and “Nightmare 5,” this music is unusual and deficient in the ambient canon for its lack of darkness, for its stubborn pacifism. It’s all yin and no yang. (Or maybe the other way around; I’m not sure.) In any case, the only place where the positivity shifts directions is during the few seconds at the end of the first track, when the piano chord suddenly turns minor before fading out. This moment is a rare and welcome surprise.

In spite of the fact that the stylistic expansions of Similes must have posed Cooper a unique set of challenges, his nearly Buddhist renunciation of tension seems to have made his job easier. Although criticizing ambient music for what it lacks is perhaps even more of a trap than getting all gushy and poetic about it, Eluvium’s glassy-eyed triumphs seem a little one-sided. During “Cease to Know,” this album’s leisurely walk into the sunset, over the course of several gorgeous minutes filled with reversing loops that feel like the night air and gentle whooshes that sound like shooting stars, I cannot help thinking that, under this record’s thick blanket of calm, something important has gone unacknowledged; something significant has been left unsaid.